Rubber compositions containing a conjugated diene polymer (e.g. polybutadiene, a butadiene-styrene copolymer) and a filler (e.g. carbon black, silica), for example, are used as rubber compositions for automobile tires. Nowadays, fuel-efficient automobiles are more and more demanded due to the public's increasing concern about environmental issues. Thus, rubber compositions for automobile tires with higher fuel economy are also desired.
Methods for enhancing fuel economy have been proposed. For example, Patent Literature 1 proposes the use of a diene rubber (modified rubber) which is modified by an organic silicon compound containing an amino group and an alkoxy group. However, the increasing concern on environmental issues nowadays demands further improved fuel economy. Moreover, other performance properties required for rubber compositions for automobile tires include wet grip performance and abrasion resistance, which are usually opposed to fuel economy. Thus, it has been difficult to provide high levels of these properties in a balanced manner.